KL-6, a sub-molecule of the glycoprotein mucin 1 (MUC1) expressed in type II pneumocytes and respiratory bronchiolar epithelial cells [29,30], plays an essential role in the pathophysiological processes of respiratory diseases; it is increased in interstitial lung diseases (most notably in the evaluation of idiopathic pulmonary fibrosis) and acute respiratory distress syndrome [14,15]. The gene discussed is MUC1; the disease is pulmonary fibrosis.